1. Field of the Invention
The present inventiFon particularly relates to a color toner for electrophotography to be preferably used for an electrophotographic method performing flash fixing, an electrostatic recording method, a magnetic recording method, or the like, and a color toner set for electrophotography using the same, a color developer for electrophotography, a method for forming a color image, and an apparatus for forming a color image.
2. Description of the Related Art
In general, for image forming in an electrophotographic system, the following processes are performed: (1) charging of a photoconductor; (2) exposure of the photoconductor to light (forming a latent image); (3) development of the latent image by a toner; (4) transfer of the toner onto a transfer material; (5) fixing of the toner onto the transfer material; and other processes. Examples of a method for fixing the toner transferred onto the transfer material may include: a method in which the toner is fused by application of pressure or heat, or by a combination thereof, and then solidified and fixed; and a method in which the toner is fused by irradiation with an optical energy, and then solidified and fixed. Recently, out of these methods, attention has been focused on oven fixing, flash fixing utilizing a light, or the like, which will not be detrimentally affected through application of pressure or heat, from the viewpoint that the method is capable of forming a fine, high-resolution image.
Namely, in these fixing methods for fixing a toner, the toner is not required to be applied with pressure. This eliminates the problem of offset, or the like, which arises in the case of a fixing roller, or the like. In consequence, these methods advantageously cause less degradation in image resolution (reproducibility) in the fixing step. Further, the toner is not required to be heated by means of a heat source or the like. This eliminates the problem that printing cannot be performed until the heat source (a fixing roller, or the like) will be preheated to a desired temperature upon power-on, or other problems. In consequence, these methods also have an advantage in that printing is possible immediately after power-on. Still further, these methods do not require a high-temperature heat source, and hence are advantageously capable of properly avoiding the temperature rising in the apparatus, or the like. Particularly, the flash fixing method also has the following advantages: even if recording paper is jammed in a fixing unit due to a system malfunction, or in other cases, the recording paper will not burn due to the heat from the heat source; and other advantages.
In general, a color toner has a low light absorption efficiency, resulting in a lower fixability as compared with a black toner. For this reason, a large number of technologies for improving the fixability by adding an infrared absorbent to the toner are proposed in, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 60-63545, 60-63546, 60-57858, 60-57857, 58-102248, 58-102247, 60-131544, 60-133460, and 61-132959, WO 99/13382, JP-A Nos. 2000-147824, 7-191492, 2000-155439, 6-348056, 10-39535, 2000-35689, 11-38666, 11-125930, 11-125928, 11-125929, and 11-65167.
However, in multicolor to full-color image forming, when multicolor toners are simultaneously fixed with the same flash energy, the toners of respective colors may have mutually different fixabilities due to a difference therebetween in type of pigment to be added to each color toner, concentration, absorbance, or the like. For this reason, even if toners are manufactured under generally the same conditions, unfavorably, it is not possible to sufficiently attain both of the fixability and the void resistance in every color toner.
Particularly, a magenta toner tends to be increased in viscosity under the influence of a pigment during toner manufacturing, unfavorably resulting in poorer fixability than that of a cyan toner or a yellow toner. For example, even if toners are manufactured under generally the same conditions, the cyan toner or the yellow toner may show better fixability as compared with the magenta toner.
In this case, if the flash energy for fixing the toner is set to be optimum condition for the cyan toner or the yellow toner, the magenta toner unfavorably shows an insufficient fixability. On the other hand, if the flash energy for fixing the toner is set to be optimum condition for the magenta toner, there occurs an excessive flash energy for the cyan toner and the yellow toner, unfavorably resulting in occurrence of voids in these toners.
Therefore, for ensuring the compatibility between fixability and the void resistance, it is important to reduce the difference in fixability between toners of respective colors as much as possible. JP-A No. 11-141347 discloses that a difference in viscosity between a monochrome toner and a color toner is caused. In this case, however, no mention is made of the problem of fixability between color toners when the magenta toner is used.